β-amylase 1 (BAM1) degrades transitory starch to sustain proline biosynthesis during drought stress

Leaf starch degradation by β-amylase ZmBAM8 influences drought tolerance in maize

As a typical C4 plant and important crop worldwide, maize is susceptible to drought. In maize, transitory starch (TS) turnover occurs in the vascular bundle sheath of leaves, differing from that in Arabidopsis (a C3 plant). This process, particularly its role in drought tolerance and the key starch-hydrolyzing enzymes involved, is not fully understood. We discovered that the expression of the β-amylase (BAM) gene ZmBAM8 is highly upregulated in the drought-tolerant inbred line Chang7-2t. Inspired by this finding, we systematically investigated TS degradation in maize lines, including Chang7-2t, Chang7-2, B104, and ZmBAM8 overexpression (OE) and knockout (KO) lines. We found that ZmBAM8 was significantly induced in the vascular bundle sheath by drought, osmotic stress, and abscisic acid. The stress-induced gene expression and chloroplast localization of ZmBAM8 align with the tissue and subcellular sites where TS turnover occurs. The recombinant ZmBAM8 was capable of effectively hydrolyzing leaf starch. Under drought conditions, the leaf starch in ZmBAM8-OE plants substantially decreased under light, while that in ZmBAM8-KO plants did not decrease. Compared with ZmBAM8-KO plants, ZmBAM8-OE plants exhibited increased drought tolerance. Our study provides insights into the significance of leaf starch degradation in C4 crops and contributes to the development of drought-resistant maize.

Molecular regulation by H2S of antioxidant and glucose metabolism in cold-sensitive Capsicum

BACKGROUND

Cold is an important environmental limiting factor affecting plant yield and quality. Capsicum (chili pepper), a tropical and subtropical vegetable crop, is extremely sensitive to cold. Although H2S is an important signaling regulator in the responses of plant growth and development to abiotic stress, few studies have examined its effects on cold-sensitive capsicum varieties. Through biotechnology methods to enhance the cold resistance of peppers, to provide some reference for pepper breeding, investigated molecular regulation by H2S of responses to cold stress in cold-sensitive capsicum plants, via physiological and transcriptomic analyses.

RESULTS

In capsicum seedlings, exogenous H2S enhanced relative electrical conductivity (REC) and levels of malondialdehyde (MDA) under cold stress, maintained membrane integrity, increased the activity of enzymatic and non-enzymatic antioxidants, balanced reactive oxygen species levels (O2·- and H2O2), and improved photosynthesis, mitigating the damage caused by cold. In addition, 416 differentially expressed genes (DEGs) were involved in the response to cold stress after H2S treatment. These DEGs were mainly enriched in the ascorbate-glutathione and starch-sucrose metabolic pathways and plant hormone signal-transduction pathways. Exogenous H2S altered the expression of key enzyme-encoding genes such as GST, APX, and MDHAR in the ascorbate-glutathione metabolism pathway, as well as that of regulatory genes for stimulatory hormones (auxin, cytokinins, and gibberellins) and inhibitory hormones (including jasmonate and salicylic acid) in the plant hormone signal-transduction pathway, helping to maintain the energy supply and intracellular metabolic stability under cold stress.

CONCLUSIONS

These findings reveal that exogenous H2S improves cold tolerance in cold-sensitive capsicum plants, elucidating the molecular mechanisms underlying its responses to cold stress. This study provides a theoretical basis for exploring and improving cold tolerance in capsicum plants.

An integration of physiology, transcriptomics, and proteomics reveals carbon and nitrogen metabolism responses in alfalfa (Medicago sativa L.) exposed to titanium dioxide nanoparticles

Nanoparticle (NP) pollution has negative impacts and is a major global environmental problem. However, the molecular response of alfalfa (Medicago sativa L.) to titanium dioxide nanoparticles (TiO2 NPs) is limited. Herein, the dual effects of TiO2 NPs (0-1000 mg L-1) on carbon (C) and nitrogen (N) metabolisms in alfalfa were investigated. The results showed that 500 mg L-1 TiO2 NPs (Ti-500) had the highest phytotoxicity in the C/N metabolizing enzymes; and it significantly increased total soluble sugar, starch, sucrose, and sucrose-phosphate synthase. Furthermore, obvious photosynthesis responses were found in alfalfa exposed to Ti-500. By contrast, 100 mg L-1 TiO2 NPs (Ti-100) enhanced N metabolizing enzymes. RNA-seq analyses showed 4265 and 2121 differentially expressed genes (DEGs) in Ti-100 and Ti-500, respectively. A total of 904 and 844 differentially expressed proteins (DEPs) were identified in Ti-100 and Ti-500, respectively. Through the physiological, transcriptional, and proteomic analyses, the DEGs and DEPs related to C/N metabolism, photosynthesis, chlorophyll synthesis, starch and sucrose metabolism, and C fixation in photosynthetic organisms were observed. Overall, TiO2 NPs at low doses improve photosynthesis and C/N regulation, but high doses can cause toxicity. It is valuable for the safe application of NPs in agriculture.

NMR Fingerprinting of Conventional and Genetically Modified Soybean Plants with AtAREB1 Transcription Factors

Drought stress impacts soybean yields and physiological processes. However, the insertion of the activated form of the AtAREB1 gene in the soybean cultivar BR16, which is sensitive to water deficit, improved the drought response of the genetically modified plants. Thus, in this study, we used 1H NMR in solution and solid-state NMR to investigate the response of genetically modified soybean overexpressing AtAREB1 under water deficiency conditions. We achieved that drought-tolerant soybean yields high content of amino acids isoleucine, leucine, threonine, valine, proline, glutamate, aspartate, asparagine, tyrosine, and phenylalanine after 12 days of drought stress conditions, as compared to drought-sensitive soybean under the same conditions. Specific target compounds, including sugars, organic acids, and phenolic compounds, were identified as involved in controlling sensitive soybean during the vegetative stage. Solid-state NMR was used to study the impact of drought stress on starch and cellulose contents in different soybean genotypes. The findings provide insights into the metabolic adjustments of soybean overexpressing AREB transcription factors in adapting to dry climates. This study presents NMR techniques for investigating the metabolome of transgenic soybean plants in response to the water deficit. The approach allowed for the identification of physiological and morphological changes in drought-resistant and drought-tolerant soybean tissues. The findings indicate that drought stress significantly alters micro- and macromolecular metabolism in soybean plants. Differential responses were observed among roots and leaves as well as drought-tolerant and drought-sensitive cultivars, highlighting the complex interplay between overexpressed transcription factors and drought stress in soybean plants.

Synergistic effects of melatonin and 24-epibrassinolide on chickpea water deficit tolerance

BACKGROUND

Water deficiency stress reduces yield in grain legumes, primarily due to a decrease in the pods number. Melatonin (ML) and 24-epibrassinolide (EBL) are recognized for their hormone-like properties that improve plant tolerance to abiotic stresses. This study aimed to assess the impact of different concentrations of ML (0, 100, and 200 µM) and EBL (0, 3, and 6 µM) on the growth, biochemical, and physiological characteristics of chickpea plants under water-stressed conditions.

RESULTS

The study's findings indicated that under water-stressed conditions, a decrease in seed (30%) and pod numbers (31%), 100-seed weight (17%), total chlorophyll content (46%), stomatal conductance (33%), as well as an increase in H2O2 (62%), malondialdehyde content (40%), and electrolyte leakage index (40%), resulted in a 40% reduction in chickpea plants grain yield. Our findings confirmed that under water-stressed conditions, seed oil, seed oil yield, and seed protein yield dropped by 20%, 55%, and 36%, respectively. The concurrent exogenous application of ML and EBL significantly reduces oxidative stress, plasma membrane damage, and reactive oxygen species (ROS) content. This treatment also leads to increased yield and its components, higher pigment content, enhanced oil and protein yield, and improved enzymatic and non-enzymatic antioxidant activities such as catalase, superoxide dismutase, polyphenol oxidase, ascorbate peroxidase, guaiacol peroxidase, flavonoid, and carotenoid. Furthermore, it promotes the accumulation of osmoprotectants such as proline, total soluble protein, and sugars.

CONCLUSIONS

Our study found that ML and EBL act synergistically to regulate plant growth, photosynthesis, osmoprotectants accumulation, antioxidant defense systems, and maintain ROS homeostasis, thereby mitigating the adverse effects of water deficit conditions. ML and EBL are key regulatory network components in stressful conditions, with significant potential for future research and practical applications. The regulation metabolic pathways of ML and EBL in water-stressed remains unknown. As a result, future research should aim to elucidate the molecular mechanisms by employing genome editing, RNA sequencing, microarray, transcriptomic, proteomic, and metabolomic analyses to identify the mechanisms involved in plant responses to exogenous ML and EBL under water deficit conditions. Furthermore, the economical applications of synthetic ML and EBL could be an interesting strategy for improving plant tolerance.

Adaptive divergence, historical population dynamics, and simulation of suitable distributions for Picea Meyeri and P. Mongolica at the whole-genome level

The taxonomic classification of Picea meyeri and P. mongolica has long been controversial. To investigate the genetic relatedness, evolutionary history, and population history dynamics of these species, genotyping-by-sequencing (GBS) technology was utilized to acquire whole-genome single nucleotide polymorphism (SNP) markers, which were subsequently used to assess population structure, population dynamics, and adaptive differentiation. Phylogenetic and population structural analyses at the genomic level indicated that although the ancestor of P. mongolica was a hybrid of P. meyeri and P. koraiensis, P. mongolica is an independent Picea species. Additionally, P. mongolica is more closely related to P. meyeri than to P. koraiensis, which is consistent with its geographic distribution. There were up to eight instances of interspecific and intraspecific gene flow between P. meyeri and P. mongolica. The P. meyeri and P. mongolica effective population sizes generally decreased, and Maxent modeling revealed that from the Last Glacial Maximum (LGM) to the present, their habitat areas decreased initially and then increased. However, under future climate scenarios, the habitat areas of both species were projected to decrease, especially under high-emission scenarios, which would place P. mongolica at risk of extinction and in urgent need of protection. Local adaptation has promoted differentiation between P. meyeri and P. mongolica. Genotype‒environment association analysis revealed 96,543 SNPs associated with environmental factors, mainly related to plant adaptations to moisture and temperature. Selective sweeps revealed that the selected genes among P. meyeri, P. mongolica and P. koraiensis are primarily associated in vascular plants with flowering, fruit development, and stress resistance. This research enhances our understanding of Picea species classification and provides a basis for future genetic improvement and species conservation efforts.

Overexpression of VaBAM3 from Vitis amurensis enhances seedling cold tolerance by promoting soluble sugar accumulation and reactive oxygen scavenging

KEY MESSAGE

The VaBAM3 cloned from Vitis amurensis can enhance the cold tolerance of overexpressed plants, but VaBAM3 knock out by CRISPR/Cas9 system weakened grape callus cold tolerance. In grape production, extreme cold conditions can seriously threaten plant survival and fruit quality. Regulation of starch content by β-amylase (BAM, EC: 3.2.1.2) contributes to cold tolerance in plants. In this study, we cloned the VaBAM3 gene from an extremely cold-tolerant grape, Vitis amurensis, and overexpressed it in tomato and Arabidopsis plants, as well as in grape callus for functional characterization. After exposure to cold stress, leaf wilting in the VaBAM3-overexpressing tomato plants was slightly less pronounced than that in wild-type tomato plants, and these plants were characterized by a significant accumulation of autophagosomes. Additionally, the VaBAM3-overexpressing Arabidopsis plants had a higher freezing tolerance than the wild-type counterparts. Under cold stress conditions, the activities of total amylase, BAM, peroxidase, superoxide dismutase, and catalase in VaBAM3-overexpressing plants were significantly higher than those in the corresponding wild-type plants. Furthermore, sucrose, glucose, and fructose contents in these lines were similarly significantly higher, whereas starch contents were reduced in comparison to the levels in the wild-type plants. Furthermore, we detected high CBF and COR gene expression levels in cold-stressed VaBAM3-overexpressing plants. Compared with those in VaBAM3-overexpressing grape callus, the aforementioned indicators tended to change in the opposite direction in grape callus with silenced VaBAM3. Collectively, our findings indicate that heterologous overexpression of VaBAM3 enhanced cold tolerance of plants by promoting the accumulation of soluble sugars and scavenging of excessive reactive oxygen species. These findings provide a theoretical basis for the cultivation of cold-resistant grape and support creation of germplasm resources for this purpose.

Mechanisms of Spirodela polyrhiza tolerance to FGD wastewater-induced heavy-metal stress: Lipidomics, transcriptomics, and functional validation

Unlike terrestrial angiosperm plants, the freshwater aquatic angiosperm duckweed (Spirodela polyrhiza) grows directly in water and has distinct responses to heavy-metal stress. Plantlets accumulate metabolites, including lipids and carbohydrates, under heavy-metal stress, but how they balance metabolite levels is unclear, and the gene networks that mediate heavy-metal stress responses remain unknown. Here, we show that heavy-metal stress induced by flue gas desulfurization (FGD) wastewater reduces chlorophyll contents, inhibits growth, reduces membrane lipid biosynthesis, and stimulates membrane lipid degradation in S. polyrhiza, leading to triacylglycerol and carbohydrate accumulation. In FGD wastewater-treated plantlets, the degraded products of monogalactosyldiacylglycerol, primarily polyunsaturated fatty acids (18:3), were incorporated into triacylglycerols. Genes involved in early fatty acid biosynthesis, β-oxidation, and lipid degradation were upregulated while genes involved in cuticular wax biosynthesis were downregulated by treatment. The transcription factor gene WRINKLED3 (SpWRI3) was upregulated in FGD wastewater-treated plantlets, and its ectopic expression increased tolerance to FGD wastewater in transgenic Arabidopsis (Arabidopsis thaliana). Transgenic Arabidopsis plants showed enhanced glutathione and lower malondialdehyde contents under stress, suggesting that SpWRI3 functions in S. polyrhiza tolerance of FGD wastewater-induced heavy-metal stress. These results provide a basis for improving heavy metal-stress tolerance in plants for industrial applications.

Rhizobium symbiosis improves amino acid and secondary metabolite biosynthesis of tungsten-stressed soybean (Glycine max)

The industrially important transition metal tungsten (W) shares certain chemical properties with the essential plant micronutrient molybdenum and inhibits the activity of molybdoenzymes such as nitrate reductase, impacting plant growth. Furthermore, tungsten appears to interfere with metabolic processes on a much wider scale and to trigger common heavy metal stress response mechanisms. We have previously found evidence that the tungsten stress response of soybeans (Glycine max) grown with symbiotically associated N2-fixing rhizobia (Bradyrhizobium japonicum) differs from that observed in nitrogen-fertilized soy plants. This study aimed to investigate how association with symbiotic rhizobia affects the primary and secondary metabolite profiles of tungsten-stressed soybean and whether changes in metabolite composition enhance the plant's resilience to tungsten. This comprehensive metabolomic and proteomic study presents further evidence that the tungsten-stress response of soybean plants is shaped by associated rhizobia. Symbiotically grown plants (N fix) were able to significantly increase the synthesis of an array of protective compounds such as phenols, polyamines, gluconic acid, and amino acids such as proline. This resulted in a higher antioxidant capacity, reduced root-to-shoot translocation of tungsten, and, potentially, also enhanced resilience of N fix plants compared to non-symbiotic counterparts (N fed). Taken together, our study revealed a symbiosis-specific metabolic readjustment in tungsten-stressed soybean plants and contributed to a deeper understanding of the mechanisms involved in the rhizobium-induced systemic resistance in response to heavy metals.

Low Nitrogen Input Mitigates Quantitative but Not Qualitative Reconfiguration of Leaf Primary Metabolism in Brassica napus L. Subjected to Drought and Rehydration

In the context of climate change and the reduction of mineral nitrogen (N) inputs applied to the field, winter oilseed rape (WOSR) will have to cope with low-N conditions combined with water limitation periods. Since these stresses can significantly reduce seed yield and seed quality, maintaining WOSR productivity under a wide range of growth conditions represents a major goal for crop improvement. N metabolism plays a pivotal role during the metabolic acclimation to drought in Brassica species by supporting the accumulation of osmoprotective compounds and the source-to-sink remobilization of nutrients. Thus, N deficiency could have detrimental effects on the acclimation of WOSR to drought. Here, we took advantage of a previously established experiment to evaluate the metabolic acclimation of WOSR during 14 days of drought, followed by 8 days of rehydration under high- or low-N fertilization regimes. For this purpose, we selected three leaf ranks exhibiting contrasted sink/source status to perform absolute quantification of plant central metabolites. Besides the well-described accumulation of proline, we observed contrasted accumulations of some "respiratory" amino acids (branched-chain amino acids, lysineand tyrosine) in response to drought under high- and low-N conditions. Drought also induced an increase in sucrose content in sink leaves combined with a decrease in source leaves. N deficiency strongly decreased the levels of major amino acids and subsequently the metabolic response to drought. The drought-rehydration sequence identified proline, phenylalanine, and tryptophan as valuable metabolic indicators of WOSR water status for sink leaves. The results were discussed with respect to the metabolic origin of sucrose and some amino acids in sink leaves and the impact of drought on source-to-sink remobilization processes depending on N nutrition status. Overall, this study identified major metabolic signatures reflecting a similar response of oilseed rape to drought under low- and high-N conditions.

OsGEX3 affects anther development and improves osmotic stress tolerance in rice

MAIN CONCLUSION

Overexpression and loss of function of OsGEX3 reduce seed setting rates and affect pollen fertility in rice. OsGEX3 positively regulates osmotic stress response by regulating ROS scavenging. GEX3 proteins are conserved in plants. AtGEX3 encodes a plasma membrane protein that plays a crucial role in pollen tube guidance. However, the function of its homolog in rice, OsGEX3, has not been determined. Our results demonstrate that OsGEX3 is localized in the plasma membrane and the nucleus as shown by a transiently transformed assay using Nicotiana benthamiana leaves. The up-regulation of OsGEX3 was detected in response to treatments with polyethylene glycol (PEG) 4000, hydrogen peroxide, and abscisic acid (ABA) via RT-qPCR analysis. Interestingly, we observed a significant decline in the seed setting rates of OsGEX3-OE lines and mutants, compared to the wild type. Further investigations reveal that overexpression and loss of function of OsGEX3 affect pollen maturation. TEM observation revealed a significant decrease in the fertile pollen rates of OsGEX3-OE transgenic lines and Osgex3 mutants due to a delay in pollen development at the late vacuolated stage. Overexpression of OsGEX3 improved osmotic stress and oxidative stress tolerance by enhancing reactive oxygen species (ROS) scavenging in rice seedlings, whereas Osgex3 mutants exhibited an opposite phenotype in osmotic stress. These findings highlight the multifunctional roles of OsGEX3 in pollen development and the response to abiotic stress. The functional characterization of OsGEX3 provides a fundamental basis for rice molecular breeding and can facilitate efforts to cultivate drought resistance and yield-related varieties.

Genome-wide identification of AAAP gene family and expression analysis in response to saline-alkali stress in foxtail millet (Setaria italica L.)

Amino acid/auxin permease (AAAP) genes encode a large family of protein transporters that play important roles in various aspects of plant growth and development. Here, we performed genome-wide identification of members in the foxtail millet (Setaria italica L.) AAAP family (SiAAAP) and their saline-alkali stress-induced expression patterns, resulting in the identification of 65 SiAAAP genes, which could be divided into eight subfamilies. Except for SiAAAP65, the remaining 64 genes were located on nine chromosomes of foxtail millet. Gene structure and conserved motif analyses indicated that the members in the same subfamily are highly conserved. Gene duplication event analysis suggested that tandem duplication may be the main factor driving the expansion of this gene family, and Ka/Ks analysis indicated that all the duplicated genes have undergone purifying selection. Transcriptome analysis showed differential expression of SiAAAPs in roots, stems, leaves, and tassel inflorescence. Analysis of cis-acting elements in the promoter indicated that SiAAAPs contain stress-responsive cis-acting elements. Under saline-alkali stress, qRT-PCR analysis showed that SiAAP3, SiLHT2, and SiAAP16 were differentially expressed between salt-alkali tolerant millet variety JK3 and salt-alkali sensitive millet variety B175. These results suggest that these genes may be involved in or regulate the response to saline-alkali stress, providing a theoretical basis for further studying the function of SiAAAPs.

Foliar Application of Amino Acids and Nutrients as a Tool to Mitigate Water Stress and Stabilize Sugarcane Yield and Bioenergy Generation

Extended periods of water stress negatively affect sugarcane crop production. The foliar application of supplements containing specific nutrients and/or organic molecules such as amino acids can improve sugarcane metabolism, stalk and sugar yields, and the quality of the extracted juice. The present study assessed the effectiveness of the foliar application of an abiotic stress protection complement (ASPC) composed of 18 amino acids and 5 macronutrients. The experiments were carried out in the field with two treatments and twelve replicates. The two treatments were no application of ASPC (control) and foliar application of ASPC. The foliar application of ASPC increased the activity of antioxidant enzymes. The Trolox-equivalent antioxidant capacity (DPPH) was higher in ASPC-treated plants than in control plants, reflecting higher antioxidant enzyme activity and lower malondialdehyde (MDA) levels. The level of H2O2 was 11.27 nM g-1 protein in plants treated with ASPC but 23.71 nM g-1 protein in control plants. Moreover, the application of ASPC increased stalk yield and sucrose accumulation, thus increasing the quality of the raw material. By positively stabilizing the cellular redox balance in sugarcane plants, ASPC application also increased energy generation. Therefore, applying ASPC is an effective strategy for relieving water stress while improving crop productivity.

Integrated Genomics and Transcriptomics Provide Insights into Salt Stress Response in Bacillus subtilis ACP81 from Moso Bamboo Shoot (Phyllostachys praecox) Processing Waste

Salt stress is detrimental to the survival of microorganisms, and only a few bacterial species produce hydrolytic enzymes. In this study, we investigated the expression of salt stress-related genes in the salt-tolerant bacterial strain Bacillus subtilis ACP81, isolated from bamboo shoot processing waste, at the transcription level. The results indicate that the strain could grow in 20% NaCl, and the sub-lethal concentration was 6% NaCl. Less neutral protease and higher cellulase and β-amylase activities were observed for B. subtilis ACP81 under sub-lethal concentrations than under the control concentration (0% NaCl). Transcriptome analysis showed that the strain adapted to high-salt conditions by upregulating the expression of genes involved in cellular processes (membrane synthesis) and defense systems (flagellar assembly, compatible solute transport, glucose metabolism, and the phosphotransferase system). Interestingly, genes encoding cellulase and β-amylase-related (malL, celB, and celC) were significantly upregulated and were involved in starch and sucrose metabolic pathways, and the accumulated glucose was effective in mitigating salt stress. RT-qPCR was performed to confirm the sequencing data. This study emphasizes that, under salt stress conditions, ACP81 exhibits enhanced cellulase and β-amylase activities, providing an important germplasm resource for saline soil reclamation and enzyme development.

Comprehensive Identification of the β-Amylase (BAM) Gene Family in Response to Cold Stress in White Clover

White clover (Trifolium repens L.) is an allopolyploid plant and an excellent perennial legume forage. However, white clover is subjected to various stresses during its growth, with cold stress being one of the major limiting factors affecting its growth and development. Beta-amylase (BAM) is an important starch-hydrolyzing enzyme that plays a significant role in starch degradation and responses to environmental stress. In this study, 21 members of the BAM gene family were identified in the white clover genome. A phylogenetic analysis using BAMs from Arabidopsis divided TrBAMs into four groups based on sequence similarity. Through analysis of conserved motifs, gene duplication, synteny analysis, and cis-acting elements, a deeper understanding of the structure and evolution of TrBAMs in white clover was gained. Additionally, a gene regulatory network (GRN) containing TrBAMs was constructed; gene ontology (GO) annotation analysis revealed close interactions between TrBAMs and AMY (α-amylase) and DPE (4-alpha-glucanotransferase). To determine the function of TrBAMs under various tissues and stresses, RNA-seq datasets were analyzed, showing that most TrBAMs were significantly upregulated in response to biotic and abiotic stresses and the highest expression in leaves. These results were validated through qRT-PCR experiments, indicating their involvement in multiple gene regulatory pathways responding to cold stress. This study provides new insights into the structure, evolution, and function of the white clover BAM gene family, laying the foundation for further exploration of the functional mechanisms through which TrBAMs respond to cold stress.

Melatonin-regulated heat shock proteins and mitochondrial ATP synthase induce drought tolerance through sustaining ROS homeostasis in H2S-dependent manner

Drought is thought to be one of the major global hazards to crop production. Understanding the role of melatonin (Mel) during plant adaptive responses to drought stress (DS) was the aim of the current investigation. Involvement of hydrogen sulfide (H2S) was also explored in Mel-regulated mechanisms of plants' tolerance to DS. A perusal of the data shows that exposure of tomato plants to DS elevated the activity of mitochondrial enzymes viz. pyruvate dehydrogenase, malate dehydrogenase, and citrate synthase. Whereas the activity of ATP synthase and ATPase was downregulated under stress conditions. Under DS, an increase in the expression level of heat shock proteins (HSPs) and activation level of antioxidant defense system was observed as well. On the other hand, an increase in the activity of NADPH oxidase and glycolate oxidase was observed along with the commencement of oxidative stress and accompanying damage. Application of 30 μM Mel to drought-stressed plants enhanced H2S accumulation and further elevated the activity of mitochondrial enzymes, activation level of the defense system, and expression of HSP17.6 and HSP70. Positive effect of Mel on these attributes was reflected by reduced level of ROS and related damage. However, application of H2S biosynthesis inhibitor DL-propargylglycine reversed the effect of Mel on the said attributes and again the damaging effects of drought were observed even in presence of Mel. This observation led us to conclude that Mel-regulated defense mechanisms operate through endogenous H2S under DS conditions.

Genome-Wide Identification and Preliminary Functional Analysis of BAM (β-Amylase) Gene Family in Upland Cotton

The β-amylase (BAM) gene family encodes important enzymes that catalyze the conversion of starch to maltose in various biological processes of plants and play essential roles in regulating the growth and development of multiple plants. So far, BAMs have been extensively studied in Arabidopsis thaliana (A. thaliana). However, the characteristics of the BAM gene family in the crucial economic crop, cotton, have not been reported. In this study, 27 GhBAM genes in the genome of Gossypium hirsutum L (G. hirsutum) were identified by genome-wide identification, and they were divided into three groups according to sequence similarity and phylogenetic relationship. The gene structure, chromosome distribution, and collinearity of all GhBAM genes identified in the genome of G. hirsutum were analyzed. Further sequence alignment of the core domain of glucosyl hydrolase showed that all GhBAM family genes had the glycosyl hydrolase family 14 domain. We identified the BAM gene GhBAM7 and preliminarily investigated its function by transcriptional sequencing analysis, qRT-PCR, and subcellular localization. These results suggested that the GhBAM7 gene may influence fiber strength during fiber development. This systematic analysis provides new insight into the transcriptional characteristics of BAM genes in G. hirsutum. It may lay the foundation for further study of the function of these genes.

Effects of drought and rehydration on root gene expression in seedlings of Pinus massoniana Lamb

The mechanisms underlying plant response to drought involve the expression of numerous functional and regulatory genes. Transcriptome sequencing based on the second- and/or third-generation high-throughput sequencing platforms has proven to be powerful for investigating the transcriptional landscape under drought stress. However, the full-length transcriptomes related to drought responses in the important conifer genus Pinus L. remained to be delineated using the third-generation sequencing technology. With the objectives of identifying the candidate genes responsible for drought and/or rehydration and clarifying the expression profile of key genes involved in drought regulation, we combined the third- and second-generation sequencing techniques to perform transcriptome analysis on seedling roots under drought stress and rewatering in the drought-tolerant conifer Pinus massoniana Lamb. A sum of 294,114 unique full-length transcripts were produced with a mean length of 3217 bp and N50 estimate of 5075 bp, including 279,560 and 124,438 unique full-length transcripts being functionally annotated and Gene Ontology enriched, respectively. A total of 4076, 6295 and 18,093 differentially expressed genes (DEGs) were identified in three pair-wise comparisons of drought-treatment versus control transcriptomes, including 2703, 3576 and 8273 upregulated and 1373, 2719 and 9820 downregulated DEGs, respectively. Moreover, 157, 196 and 691 DEGs were identified as transcription factors in the three transcriptome comparisons and grouped into 26, 34 and 44 transcription factor families, respectively. Gene Ontology enrichment analysis revealed that a remarkable number of DEGs were enriched in soluble sugar-related and cell wall-related processes. A subset of 75, 68 and 97 DEGs were annotated to be associated with starch, sucrose and raffinose metabolism, respectively, while 32 and 70 DEGs were associated with suberin and lignin biosynthesis, respectively. Weighted gene co-expression network analysis revealed modules and hub genes closely related to drought and rehydration. This study provides novel insights into root transcriptomic changes in response to drought dynamics in Masson pine and serves as a fundamental work for further molecular investigation on drought tolerance in conifers.

Sesame (Sesamum indicum L.) response to drought stress: susceptible and tolerant genotypes exhibit different physiological, biochemical, and molecular response patterns

Drought is one of the main environmental stresses affecting the quality and quantity of sesame production worldwide. The present study was conducted to investigate the effect of drought stress and subsequent re-watering on physiological, biochemical, and molecular responses of two contrasted sesame genotypes (susceptible vs. tolerant). Results showed that plant growth, photosynthetic rate, stomatal conductance, transpiration rate, and relative water content were negatively affected in both genotypes during water deficit. Both genotypes accumulated more soluble sugars, free amino acids, and proline and exhibited an increased enzyme activity for peroxidase, catalase, superoxide dismutase, and pyruvate dehydrogenase in response to drought damages including increased lipid peroxidation and membrane disruption. However, the tolerant genotype revealed a more extended root system and a more efficient photosynthetic apparatus. It also accumulated more soluble sugars (152%), free amino acids (48%), proline (75%), and antioxidant enzymes while showing lower electrolyte leakage (26%), lipid peroxidation (31%), and starch (35%) content, compared to the susceptible genotype at severe drought. Moreover, drought-related genes such as MnSOD1, MnSOD2, and PDHA-M were more expressed in the tolerant genotype, which encode manganese-dependent superoxide dismutase and the alpha subunit of pyruvate dehydrogenase, respectively. Upon re-watering, tolerant genotype recovered to almost normal levels of photosynthesis, carboxylation efficiency, lipid peroxidation, and electrolyte leakage, while susceptible genotype still suffered critical issues. Overall, these results suggest that a developed root system and an efficient photosynthetic apparatus along with the timely and effective accumulation of protective compounds enabled the tolerant sesame to withstand stress and successfully return to a normal growth state after drought relief. The findings of this study can be used as promising criteria for evaluating genotypes under drought stress in future sesame breeding programs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01372-y.

Transcriptional reprogramming during recovery from drought stress in Eucalyptus grandis

The importance of drought as a constraint to agriculture and forestry is increasing with climate change. Genetic improvement of plants' resilience is one of the mitigation strategies to curb this threat. Although recovery from drought stress is important to long-term drought adaptation and has been considered as an indicator of dehydration tolerance in annual crops, this has not been well explored in forest trees. Thus, we aimed to investigate the physiological and transcriptional changes during drought stress and rewatering in Eucalyptus grandis W. Hill ex Maiden. We set up a greenhouse experiment where we imposed drought stress on 2-year-old seedlings and rewatered the recovery group after 17 days of drought. Our measurement of leaf stomatal conductance (gs) showed that, while gs was reduced by drought stress, it fully recovered after 5 days of rewatering. The RNA-seq analysis from stem samples revealed that genes related to known stress responses such as phytohormone and reactive oxygen species signaling were upregulated, while genes involved in metabolism and growth were downregulated due to drought stress. We observed reprogramming of signal transduction pathways and metabolic processes at 1 day of rewatering, indicating a quick response to rewatering. Our results suggest that recovery from drought stress may entail alterations in the jasmonic acid, salicylic acid, ethylene and brassinosteroid signaling pathways. Using co-expression network analysis, we identified hub genes, including the putative orthologs of ABI1, ABF2, ABF3, HAI2, BAM1, GolS2 and SIP1 during drought and CAT2, G6PD1, ADG1 and FD-1 during recovery. Taken together, by highlighting the molecular processes and identifying key genes, this study gives an overview of the mechanisms underlying the response of E. grandis to drought stress and recovery that trees may face repeatedly throughout their long life cycle. This provides a useful reference to the identification and further investigation of signaling pathways and target genes for future tree improvement.

Chromatin accessibility dynamics insight into crosstalk between regulatory landscapes in poplar responses to multiple treatments

Perennial trees develop and coordinate endogenous response signaling pathways, including their crosstalk and convergence, to cope with various environmental stresses which occur simultaneously in most cases. These processes are involved in gene transcriptional regulations that depend on dynamic interactions between regulatory proteins and corresponding chromatin regions, but the mechanisms remain poorly understood in trees. In this study, we detected chromatin regulatory landscapes of poplar under abscisic acid, methyl jasmonate, salicylic acid and sodium chloride (NaCl) treatment, through integrating ATAC-seq and RNA-seq data. Our results showed that the degree of chromatin accessibility for a given gene is closely related to its expression level. However, unlike the gene expression that shows treatment-specific response patterns, changes in chromatin accessibility exhibit high similarities under these treatments. We further proposed and experimentally validated that a homologous gene copy of RESPONSIVE TO DESICCATION 26 mediates the crosstalk between jasmonic acid and NaCl signaling pathways by directly regulating the stress-responsive genes and that circadian clock-related transcription factors like REVEILLE8 play a central role in response of poplar to these treatments. Overall, our study provides a chromatin insight into the molecular mechanism of transcription regulatory networks in response to different environmental stresses and raises the key roles of the circadian clock of poplar to adapt to adverse environments.

Relationships between some transcription factors and concordantly expressed drought stress-related genes in bread wheat

The challenge of climate change makes it mandatory to improve tolerance to drought stress in bread wheat (Triticum aestivum) via biotechnological approaches. Drought stress experiment was conducted followed by RNA-Seq analysis for leaves of two wheat cultivars namely Giza 168 and Gemmiza 10 with contrasting genotypes. Expression patterns of the regulated stress-related genes and concordantly expressed TFs were detected, then, validated via qPCR for two loss-of-function mutants in Arabidopsis background harboring mutated genes analogue to those in wheat. Drought-stress related genes were searched for concordantly expressed TFs and a total of eight TFs were shown to coexpress with 14 stress-related genes. Among these genes, one TF belongs to the zinc finger protein CONSTANS family and proved via qPCR to drive expression of a gene encoding a speculative TF namely zinc transporter 3-like and two other stress related genes encoding tryptophan synthase alpha chain and asparagine synthetase. Known functions of the two TFs under drought stress complement those of the two concordantly expressed stress-related genes, thus, it is likely that they are related. This study highlights the possibility to utilize metabolic engineering approaches to decipher and incorporate existing regulatory frameworks under drought stress in future breeding programs of bread wheat.

Arabidopsis thaliana Sucrose Phosphate Synthase A2 Affects Carbon Partitioning and Drought Response

Sucrose is essential for plants for several reasons: It is a source of energy, a signaling molecule, and a source of carbon skeletons. Sucrose phosphate synthase (SPS) catalyzes the conversion of uridine diphosphate glucose and fructose-6-phosphate to sucrose-6-phosphate, which is rapidly dephosphorylated by sucrose phosphatase. SPS is critical in the accumulation of sucrose because it catalyzes an irreversible reaction. In Arabidopsis thaliana, SPSs form a gene family of four members, whose specific functions are not clear yet. In the present work, the role of SPSA2 was investigated in Arabidopsis under both control and drought stress conditions. In seeds and seedlings, major phenotypic traits were not different in wild-type compared with spsa2 knockout plants. By contrast, 35-day-old plants showed some differences in metabolites and enzyme activities even under control conditions. In response to drought, SPSA2 was transcriptionally activated, and the divergences between the two genotypes were higher, with spsa2 showing reduced proline accumulation and increased lipid peroxidation. Total soluble sugars and fructose concentrations were about halved compared with wild-type plants, and the plastid component of the oxidative pentose phosphate pathway was activated. Unlike previous reports, our results support the involvement of SPSA2 in both carbon partitioning and drought response.

Identification of genetic and biochemical mechanisms associated with heat shock and heat stress adaptation in grain amaranths

Heat stress is poised to become a major factor negatively affecting plant performance worldwide. In terms of world food security, increased ambient temperatures are poised to reduce yields in cereals and other economically important crops. Grain amaranths are known to be productive under poor and/or unfavorable growing conditions that significantly affect cereals and other crops. Several physiological and biochemical attributes have been recognized to contribute to this favorable property, including a high water-use efficiency and the activation of a carbon starvation response. This study reports the behavior of the three grain amaranth species to two different stress conditions: short-term exposure to heat shock (HS) conditions using young plants kept in a conditioned growth chamber or long-term cultivation under severe heat stress in greenhouse conditions. The latter involved exposing grain amaranth plants to daylight temperatures that hovered around 50°C, or above, for at least 4 h during the day and to higher than normal nocturnal temperatures for a complete growth cycle in the summer of 2022 in central Mexico. All grain amaranth species showed a high tolerance to HS, demonstrated by a high percentage of recovery after their return to optimal growing conditions. The tolerance observed coincided with increased expression levels of unknown function genes previously shown to be induced by other (a)biotic stress conditions. Included among them were genes coding for RNA-binding and RNA-editing proteins, respectively. HS tolerance was also in accordance with favorable changes in several biochemical parameters usually induced in plants in response to abiotic stresses. Conversely, exposure to a prolonged severe heat stress seriously affected the vegetative and reproductive development of all three grain amaranth species, which yielded little or no seed. The latter data suggested that the usually stress-tolerant grain amaranths are unable to overcome severe heat stress-related damage leading to reproductive failure.

Efficient Accumulation of Amylopectin and Its Molecular Mechanism in the Submerged Duckweed Mutant

Large-scale use of fossil fuels has brought about increasingly serious problems of environmental pollution, development and utilization of renewable energy is one of the effective solutions. Duckweed has the advantages of fast growth, high starch content and no occupation of arable land, so it is a promising starchy energy plant. A new submerged duckweed mutant (sub-1) with abundant starch accumulation was obtained, whose content of amylopectin accounts for 84.04% of the starch granules. Compared with the wild type (Lemna aequinoctialis), the branching degree of starch in sub-1 mutant was significantly increased by 19.6%. Chain length DP 6-12, DP 25-36 and DP > 36 of amylopectin significantly decreased, while chain length DP 13-24 significantly increased. Average chain length of wild-type and sub-1 mutant starches were greater than DP 22. Moreover, the crystal structure and physical properties of starch have changed markedly in sub-1 mutant. For example, the starch crystallinity of sub-1 mutant was only 8.94%, while that of wild-type was 22.3%. Compared with wild type, water solubility of starch was significantly reduced by 29.42%, whereas swelling power significantly increased by 97.07% in sub-1 mutant. In order to further analyze the molecular mechanism of efficient accumulation of amylopectin in sub-1 mutant, metabolome and transcriptome were performed. The results showed that glucose accumulated in sub-1 mutant, then degradation of starch to glucose mainly depends on α-amylase. At night, the down-regulated β-amylase gene resulted in the inhibition of starch degradation. The starch and sucrose metabolism pathways were significantly enriched. Up-regulated expression of SUS, AGPase2, AGPase3, PYG, GPI and GYS provide sufficient substrate for starch synthesis in sub-1 mutant. From the 0H to 16H light treatment, granule-bound starch synthase (GBSS1) gene was inhibited, on the contrary, the starch branching enzyme (SBE) gene was induced. Differential expression of GBSS1 and SBE may be an important reason for the decrease ratio of amylose/amylopectin in sub-1 mutant. Taken together, our results indicated that the sub-1 mutant can accumulate the amylopectin efficiently, potentially through altering the differential expression of AGPase, GBSS1, SBE, and BAM. This study also provides theoretical guidance for creating crop germplasm with high amylopectin by means of synthetic biology in the future.

Transcriptome and anatomical studies reveal alterations in leaf thickness under long-term drought stress in tobacco

Drought is one of the foremost environmental factors that limit the growth of plants. Leaf thickness (LT) is an important quantitative trait in plant physiology. The experiment was carried out in a growth room and the plants were divided into two groups such as well-watered and drought-stressed. This work investigated leaf growth in terms of leaf surface growth and expansion rate, leaf stomata traits, LT, anticlinal growth, and leaf cell layers. The results showed that the leaf area and leaf surface expansion rate were decreased by drought stress (DS). Similarly, LT, anticlinal expansion rate, palisade and spongy tissue thickness, and their related expansion rates were also decreased at different days' time points (DTP) of DS. However, a steady increase was observed in the aforementioned parameters after 12 DTP of DS. The stomatal density increased while stomata size decreased at 3 DTP and 12 DTP (low leaf water potential and relative leaf water content at these time points) and vice versa at 24 DTP compared with the well-watered plants indicating adaptations in these traits in response to DS, and thus the leaf water status played a role in the regulation of leaf stomata traits. The cell length decreased in the upper epidermis, palisade and spongy tissues by DS up to 12 DTP led to lower LT while an increase was observed after 12 DTP that resulted in higher LT. The increase in the LT was supported by the upregulation of starch and sucrose metabolism, glycerolipid metabolism, protein processing in endoplasmic reticulum pathways at 18 DTP along with the differentially expressed genes induced that were related to cell wall remodeling (cellulose, expansin, xyloglucans) and cell expansion (auxin response factors and aquaporin). The results explain the response of leaf thickness to drought stress and show alterations in LT and leaf stomatal traits. This study might serve as a valuable source of gene information for functional studies and provide a theoretical basis to understand leaf growth in terms of leaf anatomy and leaf stomatal traits under drought stress.

Comparative transcriptomic and proteomic analysis reveals common molecular factors responsive to heat and drought stresses in sweetpotaoto (Ipomoea batatas)

Introduction

Crops are affected by various abiotic stresses, among which heat (HT) and drought (DR) stresses are the most common in summer. Many studies have been conducted on HT and DR, but relatively little is known about how drought and heat combination (DH) affects plants at molecular level.

Methods

Here, we investigated the responses of sweetpotato to HT, DR, and DH stresses by RNA-seq and data-independent acquisition (DIA) technologies, using controlled experiments and the quantification of both gene and protein levels in paired samples.

Results

Twelve cDNA libraries were created under HT, DR, and DH conditions and controls. We identified 536, 389, and 907 DEGs in response to HT, DR, and DH stresses, respectively. Of these, 147 genes were common and 447 were specifically associated with DH stress. Proteomic analysis identified 1609, 1168, and 1535 DEPs under HT, DR, and DH treatments, respectively, compared with the control, of which 656 were common and 358 were exclusive to DH stress. Further analysis revealed the DEGs/DEPs were associated with heat shock proteins, carbon metabolism, phenylalanine metabolism, starch and cellulose metabolism, and plant defense, amongst others. Correlation analysis identified 6465, 6607, and 6435 co-expressed genes and proteins under HT, DR, and DH stresses respectively. In addition, a combined analysis of the transcriptomic and proteomic data identified 59, 35, and 86 significantly co-expressed DEGs and DEPs under HT, DR, and DH stresses, respectively. Especially, top 5 up-regulated co-expressed DEGs and DEPs (At5g58770, C24B11.05, Os04g0679100, BACOVA_02659 and HSP70-5) and down-regulated co-expressed DEGs and DEPs (AN3, PMT2, TUBB5, FL and CYP98A3) were identified under DH stress.

Discussion

This is the first study of differential genes and proteins in sweetpotato under DH stress, and it is hoped that the findings will assist in clarifying the molecular mechanisms involved in sweetpotato resistance to heat and drought stress.

VaBAM1 weakens cold tolerance by interacting with the negative regulator VaSR1 to suppress β-amylase expression

Cold stress is a key climatic factor that limits grape productivity and quality. Although β-amylase (BAM) is known to play an important role as a mediator of starch degradation under conditions of cold stress, the mechanism by which BAM regulates cold tolerance in grape remains unclear. Here, we identified VaBAM1 from Vitis amurensis and characterized its interactive regulating mechanism under cold stress in Arabidopsis thaliana and grape. VaBAM1-overexpressing A. thaliana plants (OEs) exhibited high freezing tolerance. Soluble sugar content and amylase activity were increased in OEs and VaBAM1-overexpressing grape calli (VaBAM1-OEs) under cold stress; however, they were decreased in grape calli in which VaBAM1 was edited using CRISPR/Cas9. The results of yeast two-hybrid, bimolecular fluorescence complementation, and pull-down experiments showed that serine/arginine-rich splicing factor 1 (VaSR1) interacted with VaBAM1. Furthermore, the expression of VaSR1 was opposite that of VaBAM1 in phloem tissue of Vitis amurensis during winter dormancy. In VaSR1-overexpressing grape calli (VaSR1-OEs), BAM activity and the expression levels of C-repeat binding transcription factor and cold response genes were all significantly lower than that in untransformed calli subjected to cold stress. Moreover, VvBAM1 was downregulated in VaSR1-OEs under cold stress. Overall, we identified that VaSR1 interacts with VaBAM1, negatively regulating BAM activity and resulting in decreased plant cold tolerance.

Co-Overexpression of Two Key Source Genes, OsBMY4 and OsISA3, Improves Multiple Key Traits of Rice Seeds

Optimized source-sink interactions are determinants of both rice yield and quality. However, most source genes have not been well studied in rice, a major grain crop. In this study, OsBMY4 and OsISA3, the key β-amylase and debranching enzymes that control transient starch degradation in rice leaves, were co-overexpressed in rice in order to accelerate starch degradation efficiency and increase the sugar supply for sink organs. Systematic analyses of the transgenic rice indicated that co-overexpression of OsBMY4 and OsISA3 not only promoted rice yield and quality, but also improved seed germination and stress tolerance. Moreover, since the OsBMY4 gene has not been characterized, we generated osbmy4 mutants using CRIPSR/Cas9 gene editing, which helped to reveal the roles of β-amylase in rice yield and quality. This study demonstrated that specific modulation of the expression of some key source genes improves the source-sink balance and leads to improvements in multiple key traits of rice seeds.

Transcription factors ABF4 and ABR1 synergistically regulate amylase-mediated starch catabolism in drought tolerance

β-Amylase (BAM)-mediated starch degradation is a main source of soluble sugars that help plants adapt to environmental stresses. Here, we demonstrate that dehydration-induced expression of PtrBAM3 in trifoliate orange (Poncirus trifoliata (L.) Raf.) functions positively in drought tolerance via modulation of starch catabolism. Two transcription factors, PtrABF4 (P. trifoliata abscisic acid-responsive element-binding factor 4) and PtrABR1 (P. trifoliata ABA repressor 1), were identified as upstream transcriptional activators of PtrBAM3 through yeast one-hybrid library screening and protein-DNA interaction assays. Both PtrABF4 and PtrABR1 played a positive role in plant drought tolerance by modulating soluble sugar accumulation derived from BAM3-mediated starch decomposition. In addition, PtrABF4 could directly regulate PtrABR1 expression by binding to its promoter, leading to a regulatory cascade to reinforce the activation of PtrBAM3. Moreover, PtrABF4 physically interacted with PtrABR1 to form a protein complex that further promoted the transcriptional regulation of PtrBAM3. Taken together, our finding reveals that a transcriptional cascade composed of ABF4 and ABR1 works synergistically to upregulate BAM3 expression and starch catabolism in response to drought condition. The results shed light on the understanding of the regulatory molecular mechanisms underlying BAM-mediated soluble sugar accumulation for rendering drought tolerance in plants.

Comprehensive genomic identification of cotton starch synthase genes reveals that GhSS9 regulates drought tolerance

Introduction

Starch metabolism is involved in the stress response. Starch synthase (SS) is the key enzyme in plant starch synthesis, which plays an indispensable role in the conversion of pyrophosphoric acid to starch. However, the SS gene family in cotton has not been comprehensively identified and systematically analyzed.

Result

In our study, a total of 76 SS genes were identified from four cotton genomes and divided into five subfamilies through phylogenetic analysis. Genetic structure analysis proved that SS genes from the same subfamily had similar genetic structure and conserved sequences. A cis-element analysis of the SS gene promoter showed that it mainly contains light response elements, plant hormone response elements, and abiotic stress elements, which indicated that the SS gene played key roles not only in starch synthesis but also in abiotic stress response. Furthermore, we also conducted a gene interaction network for SS proteins. Silencing GhSS9 expression decreased the resistance of cotton to drought stress. These findings suggested that SS genes could be related to drought stress in cotton, which provided theoretical support for further research on the regulation mechanism of SS genes on abiotic starch synthesis and sugar levels.

Exogenous 24-epibrassinolide boosts plant growth under alkaline stress from physiological and transcriptomic perspectives: The case of broomcorn millet (Panicum miliaceum L.)

Land alkalization is an abiotic stress that affects global sustainable agricultural development and the balance of natural ecosystems. In this study, two broomcorn millet cultivars, T289 (alkaline-tolerant) and S223 (alkaline-sensitive), were selected to investigate the response of broomcorn millet to alkaline stress and the role of brassinolide (BR) in alkaline tolerance. Phenotypes, physiologies, and transcriptomes of T289 and S223 plants under only alkaline stress (AS) and alkaline stress with BR (AB) were compared. The results showed that alkaline stress inhibited growth, promoted the accumulation of soluble sugars and malondialdehyde, enhanced electrolyte leakage, and destroyed the integrity of broomcorn millet stomata. In contrast, BR lessened the negative effects of alkaline stress on plants. Transcriptome sequencing analysis showed that relative to control groups (CK, nutrient solution), in AS groups, 21,113 and 12,151 differentially expressed genes (DEGs) were identified in S223 and T289, respectively. Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed various terms and pathways related to metabolism. Compared to S223, alkaline stress strongly activated the brassinosteroid biosynthesis pathway in T289. Conversely, ARF, TF, and TCH4, associated with cell growth and elongation, were inhibited by alkaline stress in S223. Moreover, alkaline stress induced the activation of the mitogen-activated protein kinase (MAPK) pathway, the abscisic acid signaling pathway that initiates stomatal closure, as well as the starch and sucrose metabolism. The EG and BGL genes, which are associated with cellulose degradation, were notably activated. BR enhanced alkaline tolerance, thereby alleviating the transcriptional responses of the two cultivars. Cultivar T289 is better in alkalized regions. Taken together, these results reveal how broomcorn millet responds to alkaline stress and BR mitigates alkaline stress, thus promoting agriculture in alkalized regions.

Changing winter climate and snow conditions induce various transcriptional stress responses in Scots pine seedlings

In northern boreal forests the warming winter climate leads to more frequent snowmelt, rain-on-snow events and freeze-thaw cycles. This may be harmful or even lethal for tree seedlings that spend even a half of the year under snow. We conducted a snow cover manipulation experiment in a natural forest to find out how changing snow conditions affect young Scots pine (Pinus sylvestris L.) seedlings. The ice encasement (IE), absence of snow (NoSNOW) and snow compaction (COMP) treatments affected ground level temperature, ground frost and subnivean gas concentrations compared to the ambient snow cover (AMB) and led to the increased physical damage and mortality of seedlings. The expression responses of 28 genes related to circadian clock, aerobic and anaerobic energy metabolism, carbohydrate metabolism and stress protection revealed that seedlings were exposed to different stresses in a complex way depending on the thickness and quality of the snow cover. The IE treatment caused hypoxic stress and probably affected roots which resulted in reduced water uptake in the beginning of the growing season. Without protective snowpack in NoSNOW seedlings suffered from cold and drought stresses. The combination of hypoxic and cold stresses in COMP evoked unique transcriptional responses including oxidative stress. Snow cover manipulation induced changes in the expression of several circadian clock related genes suggested that photoreceptors and the circadian clock system play an essential role in the adaptation of Scots pine seedlings to stresses under different snow conditions. Our findings show that warming winter climate alters snow conditions and consequently causes Scots pine seedlings various abiotic stresses, whose effects extend from overwintering to the following growing season.

Overexpression of DoBAM1 from Yam (Dioscorea opposita Thunb.) Enhances Cold Tolerance in Transgenic Tobacco

β-amylase (BAM) plays an important role in plant development and response to abiotic stresses. In this study, 5 DoBAM members were identified in yam (Dioscorea opposita Thunb.). A novel β-amylase gene BAM1, (named DoBAM1), was isolated from yam varieties Bikeqi and Dahechangyu. The open reading frame (ORF) of DoBAM1 is 2806 bp and encodes 543 amino acids. Subcellular localization analysis indicates that DoBAM1 localizes to the cell membrane and cytoplasm. In the yam variety Dahechangyu, the starch content, β-amylase activity, and expression of DoBAM1 were characterized and found to all be higher than in Bikeqi. DoBAM1 overexpression in tobacco is shown to promote the accumulation of soluble sugar and chlorophyll content and to increase the activities of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and β-amylase. Under cold treatment, we observed the induced upregulation of DoBAM1 and lower starch content and malondialdehyde (MDA) accumulation than in WT plants. In conclusion, these results demonstrate that DoBAM1 overexpression plays an advanced role in cold tolerance, at least in part by raising the levels of soluble sugars that are capable of acting as osmolytes or antioxidants.

From source to sink: mechanistic insight of photoassimilates synthesis and partitioning under high temperature and elevated [CO2]

Photosynthesis is the vital metabolism of the plant affected by abiotic stress such as high temperature and elevated [CO₂] levels, which ultimately affect the source-sink relationship. Triose phosphate, the primary precursor of carbohydrate (starch and sucrose) synthesis in the plant, depends on environmental cues. The synthesis of starch in the chloroplasts of leaves (during the day), the transport of photoassimilates (sucrose) from source to sink, the loading and unloading of photoassimilates, and the accumulation of starch in the sink tissue all require a highly regulated network and communication system within the plant. These processes might be affected by high-temperature stress and elevated [CO₂] conditions. Generally, elevated [CO₂] levels enhance plant growth, photosynthetic rate, starch synthesis, and accumulation, ultimately diluting the nutrient of sink tissues. On the contrary, high-temperature stress is detrimental to plant development affecting photosynthesis, starch synthesis, sucrose synthesis and transport, and photoassimilate accumulation in sink tissues. Moreover, these environmental conditions also negatively impact the quality attributes such as grain/tuber quality, cooking quality, nutritional status in the edible parts and organoleptic traits. In this review, we have attempted to provide an insight into the source-sink relationship and the sugar metabolites synthesized and utilized by the plant under elevated [CO₂] and high-temperature stress. This review will help future researchers comprehend the source-sink process for crop growth under changing climate scenarios.

Phosphoprotein Profile of Rice (Oryza sativa L.) Seedlings under Osmotic Stress after Pretreatment with Chitosan

This study aims to identify novel chitosan (CTS)-responsive phosphoproteins in Leung Pratew 123 (LPT123) and Khao Dawk Mali 105 (KDML105) as drought-sensitive rice cultivars and differences in the CTS response. Rice seeds were soaked in CTS solution before germination, and 2- and 4-week-old rice seedlings sprayed with CTS before osmotic stress comprised the following four groups: (1) seedlings treated with distilled water; (2) seedlings treated with CTS; (3) seedlings pretreated with distilled water and subjected to osmotic stress; and (4) seedlings pretreated with CTS and subjected to osmotic stress. Phosphoproteins of leaf tissues were enriched using immobilized metal affinity chromatography (IMAC) before tryptic digestion and analysis via LC-MS. Phosphoprotein profiling analyses led to the identification of 4721 phosphoproteins representing 1052 and 1040 unique phosphoproteins in the LPT123 and KDML105 seedlings, respectively. In response to CTS pretreatment before osmotic stress, 22 differently expressed proteins were discovered, of which 10 and 12 were identified in the LPT123 and KDML105, respectively. These proteins are typically involved in signaling, transport, protein folding, protein degradation, and metabolism. This study provides fruitful data to understand the signal transduction mechanisms of rice seedlings pretreated with CTS before exposure to osmotic stress.

Metabolic, physiological and anatomical responses of soybean plants under water deficit and high temperature condition

Water deficit (WD) combined with high temperature (HT) is the major factor limiting agriculture worldwide, and it is predicted to become worse according to the current climate change scenario. It is thus important to understand how current cultivated crops respond to these stress conditions. Here we investigated how four soybean cultivars respond to WD and HT isolated or in combination at metabolic, physiological, and anatomical levels. The WD + HT increased the level of stress in soybean plants when compared to plants under well-watered (WW), WD, or HT conditions. WD + HT exacerbates the increases in ascorbate peroxidase activity, which was associated with the greater photosynthetic rate in two cultivars under WD + HT. The metabolic responses to WD + HT diverge substantially from plants under WW, WD, or HT conditions. Myo-inositol and maltose were identified as WD + HT biomarkers and were connected to subnetworks composed of catalase, amino acids, and both root and leaf osmotic potentials. Correlation-based network analyses highlight that the network heterogeneity increased and a higher integration among metabolic, physiological, and morphological nodes is observed under stress conditions. Beyond unveiling biochemical and metabolic WD + HT biomarkers, our results collectively highlight that the mechanisms behind the acclimation to WD + HT cannot be understood by investigating WD or HT stress separately.

Physiological and molecular mechanisms of the response of roots of Pinus massoniana Lamb. to low-temperature stress

Pinus massoniana Lamb. is the timber species with the widest distribution and the largest afforestation area in China, providing a large amount of timber, turpentine and ecological products. but low temperature limits its growth and geographical distribution. Physiological and molecular studies can well explain the mechanism of P. massoniana response to low temperature. In this study, physiological and biochemical indexes, cell morphology, lignin content, gene regulatory networks, and gene expression patterns of different P. massoniana varieties (cold-tolerant and cold-sensitive) were studied from physiological, biochemical, and molecular perspectives. The results indicated that under low-temperature stress, the cold-tolerant cultivar maintained high contents of osmoregulatory substances, and the root morphology and structure remained intact. In the initial stage of low-temperature stress, the number of differentially expressed genes was 7148, and with the extension of stress time, the number of differentially expressed genes decreased to 1991. P. massoniana might direct its responses to low temperature by regulating phenylpropane metabolism, starch and sucrose metabolism, hormone signaling pathways, and transcription factors. BAM, 4CL, CCoAOMT, PRX5, WRKYs, and hormone synthesis related genes play important roles. P. massoniana cultivars may vary in response mechanisms. In this study, physiological and analytical techniques were used to study the root tip response mechanism of Masson's pine to low temperature stress. The results of this study lay a foundation for in-depth research on the molecular functions of P. massoniana under low-temperature stress conditions.

High-resolution shotgun proteomics reveals that increased air [CO2] amplifies the acclimation response of coffea species to drought regarding antioxidative, energy, sugar, and lipid dynamics

As drought threatens crop productivity it is crucial to characterize the defense mechanisms against water deficit and unveil their interaction with the expected rise in the air [CO₂]. For that, plants of Coffea canephora cv. Conilon Clone 153 (CL153) and C. arabica cv. Icatu grown under 380 (aCO₂) or 700 μL L^-1 (eCO₂) were exposed to moderate (MWD) and severe (SWD) water deficits. Responses were characterized through the activity and/or abundance of a selected set of proteins associated with antioxidative (e.g., Violaxanthin de-epoxidase, Superoxide dismutase, Ascorbate peroxidases, Monodehydroascorbate reductase), energy/sugar (e.g., Ferredoxin-NADP reductase, NADP-dependent glyceraldehyde-3-phosphate dehydrogenase, sucrose synthase, mannose-6-phosphate isomerase, Enolase), and lipid (Lineolate 13S-lipoxygenase) processes, as well as with other antioxidative (ascorbate) and protective (HSP70) molecules. MWD caused small changes in both genotypes regardless of [CO₂] level while under the single imposition to SWD, only Icatu showed a global reinforcement of most studied proteins supporting its tolerance to drought. eCO₂ alone did not promote remarkable changes but strengthened a robust multi-response under SWD, even supporting the reversion of impacts already observed by CL153 at aCO₂. In the context of climate changes where water constraints and [CO₂] levels are expected to increase, these results highlight why eCO₂ might have an important role in improving drought tolerance in Coffea species.

Tonoplast Sucrose Trafficking Modulates Starch Utilization and Water Deficit Behavior in Poplar Leaves

Leaf osmotic adjustment by the active accrual of compatible organic solutes (e.g. sucrose) contributes to drought tolerance throughout the plant kingdom. In Populus tremula x alba, PtaSUT4 encodes a tonoplast sucrose-proton symporter, whose downregulation by chronic mild drought or transgenic manipulation is known to increase leaf sucrose and turgor. While this may constitute a single drought tolerance mechanism, we now report that other adjustments which can occur during a worsening water deficit are damped when PtaSUT4 is constitutively downregulated. Specifically, we report that starch use and leaf relative water content (RWC) dynamics were compromised when plants with constitutively downregulated PtaSUT4 were subjected to a water deficit. Leaf RWC decreased more in wild-type and vector control lines than in transgenic PtaSUT4-RNAi (RNA-interference) or CRISPR (clustered regularly interspersed short palindromic repeats) knockout (KO) lines. The control line RWC decrease was accompanied by increased PtaSUT4 transcript levels and a mobilization of sucrose from the mesophyll-enriched leaf lamina into the midvein. The findings suggest that changes in SUT4 expression can increase turgor or decrease RWC as different tolerance mechanisms to reduced water availability. Evidence is presented that PtaSUT4-mediated sucrose partitioning between the vacuole and the cytosol is important not only for overall sucrose abundance and turgor, but also for reactive oxygen species (ROS) and antioxidant dynamics. Interestingly, the reduced capacity for accelerated starch breakdown under worsening water-deficit conditions was correlated with reduced ROS in the RNAi and KO lines. A role for PtaSUT4 in the orchestration of ROS, antioxidant, starch utilization and RWC dynamics during water stress and its importance in trees especially, with their high hydraulic resistances, is considered.

Characterization of the gene expression profile response to drought stress in Haloxylon using PacBio single-molecule real-time and Illumina sequencing

Haloxylon ammodendron and Haloxylon persicum are important drought-tolerant plants in northwest China. The whole-genome sequencing of H. ammodendron and H. persicum grown in their natural environment is incomplete, and their transcriptional regulatory network in response to drought environment remains unclear. To reveal the transcriptional responses of H. ammodendron and H. persicum to an arid environment, we performed single-molecule real-time (SMRT) and Illumina RNA sequencing. In total, 20,246,576 and 908,053 subreads and 435,938 and 210,334 circular consensus sequencing (CCS) reads were identified by SMRT sequencing of H. ammodendron and H. persicum, and 15,238 and 10,135 unigenes, respectively, were successfully obtained. In addition, 9,794 and 7,330 simple sequence repeats (SSRs) and 838 and 71 long non-coding RNAs were identified. In an arid environment, the growth of H. ammodendron was restricted; plant height decreased significantly; basal and branch diameters became thinner and hydrogen peroxide (H₂O₂) content and peroxidase (POD) activity were increased. Under dry and wet conditions, 11,803 and 15,217 differentially expressed genes (DEGs) were identified in H. ammodendron and H. persicum, respectively. There were 319 and 415 DEGs in the signal transduction pathways related to drought stress signal perception and transmission, including the Ca²⁺ signal pathway, the ABA signal pathway, and the MAPK signal cascade. In addition, 217 transcription factors (TFs) and 398 TFs of H. ammodendron and H. persicum were differentially expressed, including FAR1, MYB, and AP2/ERF. Bioinformatic analysis showed that under drought stress, the expression patterns of genes related to active oxygen [reactive oxygen species (ROS)] scavenging, functional proteins, lignin biosynthesis, and glucose metabolism pathways were altered. Thisis the first full-length transcriptome report concerning the responses of H. ammodendron and H. persicum to drought stress. The results provide a foundation for further study of the adaptation to drought stress. The full-length transcriptome can be used in genetic engineering research.

Rising rates of starch degradation during daytime and trehalose 6-phosphate optimize carbon availability

Many plants, including Arabidopsis (Arabidopsis thaliana), accumulate starch in the light and remobilize it to support maintenance and growth at night. Starch synthesis and degradation are usually viewed as temporally separate processes. Recently, we reported that starch is also degraded in the light. Degradation rates are generally low early in the day but rise with time. Here, we show that the rate of degradation in the light depends on time relative to dawn rather than dusk. We also show that degradation in the light is inhibited by trehalose 6-phosphate, a signal for sucrose availability. The observed responses of degradation in the light can be simulated by a skeletal model in which the rate of degradation is a function of starch content divided by time remaining until dawn. The fit is improved by extension to include feedback inhibition of starch degradation by trehalose 6-phosphate. We also investigate possible functions of simultaneous starch synthesis and degradation in the light, using empirically parameterized models and experimental approaches. The idea that this cycle buffers growth against falling rates of photosynthesis at twilight is supported by data showing that rates of protein and cell wall synthesis remain high during a simulated dusk twilight. Degradation of starch in the light may also counter over-accumulation of starch in long photoperiods and stabilize signaling around dusk. We conclude that starch degradation in the light is regulated by mechanisms similar to those that operate at night and is important for stabilizing carbon availability and signaling, thus optimizing growth in natural light conditions.

Contrasting Water Withholding Responses of Young Maize Plants Reveal Link Between Lipid Peroxidation and Osmotic Regulation Corroborated by Genetic Analysis

Linking biochemistry and genetics of tolerance to osmotic stress is of interest for understanding plant adaptations to unfavorable conditions. The aims of this study were to investigate the variability in responses of panel of elite maize inbred lines to water withholding for stress-related traits through association study and to identify pathways linked to detected associations for better understanding of maize stress responses. Densely genotyped public and expired Plant Variety Protection Certificate (ex-PVP) inbred lines were planted in controlled conditions (16-h/8-h day/night, 25°C, 50% RH) in control (CO) and exposed to 10-day water withholding (WW). Traits analyzed were guaiacol peroxidase activity (GPOD), total protein content (PROT), lipid peroxidation (TBARS), hydrogen peroxide accumulation (H₂O₂), proline accumulation (proline), and current water content (CWC). Proline accumulation was found to be influenced by H₂O₂ and TBARS signaling pathways acting as an accumulation-switching mechanism. Most of the associations detected were for proline (29.4%) and TBARS (44.1%). Gene ontology (GO) enrichment analysis showed significant enrichment in regulation of integral membrane parts and peroxisomes along with regulation of transcription and polysaccharide catabolism. Dynamic studies involving inbreds with extreme phenotypes are needed to elucidate the role of this signaling mechanism in regulation of response to water deficit.

The Sweetpotato Voltage-Gated K+ Channel β Subunit, KIbB1, Positively Regulates Low-K+ and High-Salinity Tolerance by Maintaining Ion Homeostasis

Voltage-gated K⁺ channel β subunits act as a structural component of K_in channels in different species. The β subunits are not essential to the channel activity but confer different properties through binding the T1 domain or the C-terminal of α subunits. Here, we studied the physiological function of a novel gene, KIbB1, encoding a voltage-gated K⁺ channel β subunit in sweetpotato. The transcriptional level of this gene was significantly higher in the low-K⁺-tolerant line than that in the low-K⁺-sensitive line under K⁺ deficiency conditions. In Arabidopsis, KIbB1 positively regulated low-K⁺ tolerance through regulating K⁺ uptake and translocation. Under high-salinity stress, the growth conditions of transgenic lines were obviously better than wild typr (WT). Enzymatic and non-enzymatic reactive oxygen species (ROS) scavenging were activated in transgenic plants. Accordingly, the malondialdehyde (MDA) content and the accumulation of ROS such as H₂O₂ and O²⁻ were lower in transgenic lines under salt stress. It was also found that the overexpression of KIbB1 enhanced K⁺ uptake, but the translocation from root to shoot was not affected under salt stress. This demonstrates that KIbB1 acted as a positive regulator in high-salinity stress resistance through regulating Na⁺ and K⁺ uptake to maintain K⁺/Na⁺ homeostasis. These results collectively suggest that the mechanisms of KIbB1 in regulating K⁺ were somewhat different between low-K⁺ and high-salinity conditions.

A dominant mutation in β-AMYLASE1 disrupts nighttime control of starch degradation in Arabidopsis leaves

Arabidopsis (Arabidopsis thaliana) leaves possess a mechanism that couples the rate of nighttime starch degradation to the anticipated time of dawn, thus preventing premature exhaustion of starch and nighttime starvation. To shed light on the mechanism, we screened a mutagenized population of a starvation reporter line and isolated a mutant that starved prior to dawn. The mutant had accelerated starch degradation, and the rate was not adjusted to time of dawn. The mutation responsible led to a single amino acid change (S132N) in the starch degradation enzyme BETA-AMYLASE1 (BAM1; mutant allele named bam1-2D), resulting in a dominant, gain-of-function phenotype. Complete loss of BAM1 (in bam1-1) did not affect rates of starch degradation, while expression of BAM1(S132N) in bam1-1 recapitulated the accelerated starch degradation phenotype of bam1-2D. In vitro analysis of recombinant BAM1 and BAM1(S132N) proteins revealed no differences in kinetic or stability properties, but in leaf extracts, BAM1(S132N) apparently had a higher affinity than BAM1 for an established binding partner required for normal rates of starch degradation, LIKE SEX FOUR1 (LSF1). Genetic approaches showed that BAM1(S132N) itself is likely responsible for accelerated starch degradation in bam1-2D and that this activity requires LSF1. Analysis of plants expressing BAM1 with alanine or aspartate rather than serine at position 132 indicated that the gain-of-function phenotype is not related to phosphorylation status at this position. Our results strengthen the view that control of starch degradation in wild-type plants involves dynamic physical interactions of degradative enzymes and related proteins with a central role for complexes containing LSF1.

The Memory of Rice Response to Spaceflight Stress: From the Perspective of Metabolomics and Proteomics

The stress response of plants to spaceflight has been confirmed in contemporary plants, and plants retained the memory of spaceflight through methylation reaction. However, how the progeny plants adapt to this cross-generational stress memory was rarely reported. Here, we used the ShiJian-10 retractable satellite carrying Dongnong416 rice seeds for a 12.5-day on-orbit flight and planted the F2 generation after returning to the ground. We evaluated the agronomic traits of the F2 generation plants and found that the F2 generation plants had no significant differences in plant height and number of tillers. Next, the redox state in F2 plants was evaluated, and it was found that the spaceflight broke the redox state of the F2 generation rice. In order to further illustrate the stress response caused by this redox state imbalance, we conducted proteomics and metabolomics analysis. Proteomics results showed that the redox process in F2 rice interacts with signal transduction, stress response, and other pathways, causing genome instability in the plant, leading to transcription, post-transcriptional modification, protein synthesis, protein modification, and degradation processes were suppressed. The metabolomics results showed that the metabolism of the F2 generation plants was reshaped. These metabolic pathways mainly included amino acid metabolism, sugar metabolism, cofactor and vitamin metabolism, purine metabolism, phenylpropane biosynthesis, and flavonoid metabolism. These metabolic pathways constituted a new metabolic network. This study confirmed that spaceflight affected the metabolic changes in offspring rice, which would help better understand the adaptation mechanism of plants to the space environment.

BETA-AMYLASE9 is a plastidial nonenzymatic regulator of leaf starch degradation

β-Amylases (BAMs) are key enzymes of transitory starch degradation in chloroplasts, a process that buffers the availability of photosynthetically fixed carbon over the diel cycle to maintain energy levels and plant growth at night. However, during vascular plant evolution, the BAM gene family diversified, giving rise to isoforms with different compartmentation and biological activities. Here, we characterized BETA-AMYLASE 9 (BAM9) of Arabidopsis (Arabidopsis thaliana). Among the BAMs, BAM9 is most closely related to BAM4 but is more widely conserved in plants. BAM9 and BAM4 share features including their plastidial localization and lack of measurable α-1,4-glucan hydrolyzing capacity. BAM4 is a regulator of starch degradation, and bam4 mutants display a starch-excess phenotype. Although bam9 single mutants resemble the wild-type (WT), genetic experiments reveal that the loss of BAM9 markedly enhances the starch-excess phenotypes of mutants already impaired in starch degradation. Thus, BAM9 also regulates starch breakdown, but in a different way. Interestingly, BAM9 gene expression is responsive to several environmental changes, while that of BAM4 is not. Furthermore, overexpression of BAM9 in the WT reduced leaf starch content, but overexpression in bam4 failed to complement fully that mutant's starch-excess phenotype, suggesting that BAM9 and BAM4 are not redundant. We propose that BAM9 activates starch degradation, helping to manage carbohydrate availability in response to fluctuations in environmental conditions. As such, BAM9 represents an interesting gene target to explore in crop species.

How Stress Affects Your Budget-Stress Impacts on Starch Metabolism

Starch is a polysaccharide that is stored to be used in different timescales. Transitory starch is used during nighttime when photosynthesis is unavailable. Long-term starch is stored to support vegetative or reproductive growth, reproduction, or stress responses. Starch is not just a reserve of energy for most plants but also has many other roles, such as promoting rapid stomatal opening, making osmoprotectants, cryoprotectants, scavengers of free radicals and signals, and reverting embolised vessels. Biotic and abiotic stress vary according to their nature, strength, duration, developmental stage of the plant, time of the day, and how gradually they develop. The impact of stress on starch metabolism depends on many factors: how the stress impacts the rate of photosynthesis, the affected organs, how the stress impacts carbon allocation, and the energy requirements involved in response to stress. Under abiotic stresses, starch degradation is usually activated, but starch accumulation may also be observed when growth is inhibited more than photosynthesis. Under biotic stresses, starch is usually accumulated, but the molecular mechanisms involved are largely unknown. In this mini-review, we explore what has been learned about starch metabolism and plant stress responses and discuss the current obstacles to fully understanding their interactions.

Heterografted chrysanthemums enhance salt stress tolerance by integrating reactive oxygen species, soluble sugar, and proline

Chrysanthemum, one of the most important commercial ornamental crops, is susceptible to salinity, which limits its cultivation and application in coastal and inland saline areas. Grafting is widely used to improve the salt tolerance of horticultural crops, but the mechanisms of grafted chrysanthemum responses to salt stress remain unclear. In this study, we showed that heterografted chrysanthemums with Artemisia annua as rootstock exhibited increased salt tolerance compared with self-grafted and self-rooted chrysanthemums. Under high salt stress, the roots of heterografted chrysanthemums enrich Na⁺, resulting in a reduction of Na⁺ toxicity in the scion, with only a small amount of Na⁺ being transported to the leaves. On the other hand, the roots of heterografted chrysanthemums alleviated high Na⁺ stress via enhanced catalase enzyme activity, downregulation of the expression of reactive oxygen species (ROS) accumulation-related genes, massive accumulation of soluble sugars and proline, and upregulation of the expression of heat shock protein-related genes to enhance salt tolerance. In addition, the leaves of heterografted chrysanthemums respond to low Na⁺ stress by increasing peroxidase enzyme activity and soluble sugar and proline contents, to maintain a healthy state. However, self-grafted and self-rooted plants could not integrate ROS, soluble sugars, and proline in response to salt stress, and thus exhibited a salt-sensitive phenotype. Our research reveals the mechanisms underlying the increased salt tolerance of heterografted chrysanthemums and makes it possible to have large-scale cultivation of chrysanthemums in saline areas.